The operation of an electronic device like, for example, a processor system is often influenced by the supply voltage. The maximum speed, at which a stable operation is still possible, may depend on the supply voltage. Usually the signal delays inside an electronic device are lower at higher supply voltages and thus higher operation frequencies are possible at higher voltages. The capability of a processor system to store values in internal registers or memories usually also depends on the supply voltage and gets better at higher supply voltages. At lower voltages the risk can increase that a value stored in a register or memory can be altered unintentionally. Furthermore, the power consumption in most cases is higher at higher supply voltages.
Sometimes there is a desire to operate the electronic device in different operation modes with different requirements regarding, for example, speed or power consumption. In these different operation modes, the electronic device usually operates with different supply voltages. Preferably an electronic device is operated with the lowest possible supply voltage in order to save power. The lowest possible supply voltage often depends on the operation requirements, for example regarding speed. The operation mode may be changed dynamically during operation.
Advantageously the supply voltage is monitored to determine whether it meets the requirements for the respective operation mode. For this purpose the supply voltage is compared with a reference voltage. A problem exists in monitoring the supply voltage during changes of the supply voltage since in this phase the reference voltage is also changed.